Biological wastewater treatment systems that utilize biofilm carriers or biocarriers are known. These biofilm carriers move about in a tank or reactor. During the course of a wastewater treatment process, these biofilm carriers are effective for removing contaminants or pollutants from the wastewater. Since treated wastewater must be discharged from a tank or reactor, some provision must be provided for discharging the treated wastewater and at the same time retaining the biofilm carriers.
Screen structures are used to prevent biofilm carriers from being discharged with wastewater leaving the tank or reactor. However conventional screen structures used in tanks and reactors to retain biofilm carriers include frames that consume a significant area. In some cases these frames extend into the treatment tank and impede the movement of biofilm carriers, sometimes leading to blockage of the screens.
Typical screen supports or frames are not integral with the screens. This resulted in the frames, without the screens, being mounted to the concrete wall of the tank. Securing the screen panels to the frames previously mounted to the wall is a difficult and time consuming task. Typically supports project from the wall of the tank and support both the frame structure and the screen panels that have been attached to the frame structure. Once the frame structure and screens have been mounted adjacent a wall, these supports are typically located behind the screen panels which makes inspection very difficult. Furthermore the screen support beams and columns that make up the frame structure are usually very stiff structurally and do not conform well to irregularities in a concrete wall, leading to misalignment between adjacent screen panels and sometimes requiring field modifications to the screen panels in order to mount them to the previously mounted frame.
In the end the final screen assembly is made up of many separate parts, screens, support components and hardware. Spaces or gaps that surround the screens are typically filled with imperviable strips that decrease the effective screening area.
Therefore, there has been and continues to be a need for a screen structure for use in a biological wastewater treatment system that uses biofilm carriers where the screen structure is simple and easy to install and which readily conforms to irregularities in the wall structure to which the screen modules are to be mounted.